American Board of Surgery Qualifying Exam (ABS QE) Practice Test

What nerve is most likely affected by a midshaft humerus fracture?

1. Brachial plexus

2. Radial nerve

3. Median nerve

4. Ulnar nerve

The correct answer is: Radial nerve

A midshaft humerus fracture most commonly affects the radial nerve due to the anatomical relationship between the nerve and the humerus. The radial nerve runs in the radial groove of the humerus, which is located posteriorly. When a fracture occurs in the midshaft region, the bony fragments can disrupt or compress the radial nerve, leading to characteristic symptoms. Injury to the radial nerve results in wrist drop, which is an inability to extend the wrist and fingers. This is a key clinical feature that helps identify the nerve affected following such a fracture. Understanding the anatomical pathways of these nerves is essential for diagnosis and management in clinical practice. The other nerves mentioned have different anatomical locations and would be affected by fractures in other regions. The brachial plexus is located more proximally and is not directly impacted by midshaft injuries; the median and ulnar nerves are primarily involved in injuries at the distal humerus or elbow region. Thus, the radial nerve is the most logical and clinically relevant choice in the context of a midshaft humeral fracture.